Frank j



(.No Model.)

F. J. SPRAGUH- REGULATOR FOR ELECTED DYNAMIC MOTORS.

No. 313,247. Patented Mar. 3, 1885.

010 a) OJ AT TEsiT INVENTOR:

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UNITED STATES PATENT Fries.

FRANK J. SPRAGUE, OF NEW YORK, N. Y.

REG ULATO R FOR ELECTRO- DYNAM EC MOTORS.

SPECIFICATION forming part of Letters Patent No. 313,241 dated March 3,1885,

Application filed February 21, 1884. (No model.)

To aZZ whom, it may concern:

Be it known that FRANK J. SPRAGUE, of New York, in the county and Stateof New York, have invented a certain new and useful Improvement inElectroDynamic Motors, of which the following is a specification.

My invention relates to electro-dynamic motors of that class in whichthe main fieldcoils-that is to say, those which determine the polarityof the field, are in shunt relation to the armature; and said inventionconsists in anew method of regulation for such motors, as hereinafterset forth, whereby the speed or the power of a motor may be varied, orthe speed may be maintained constant under varying loads or undervarying conditions of the circuit. My method of regulation is thereforeadapted to all the different conditions and situations in which suchmotors may be used, whether they are stationary motors connected with asystem of electrical distribution, in which case it is usually desirableto maintain a constant speed under different loads, and usually with aconstant potential circuit, or used upon moving vehicles for railwaypurposes, in which case the speed must necessarily he often changed, andalso the power, as for differing grades, and where the initial potentialchanges on account of the moving of the motor to different parts of thecircuit, and from other causes.

The main features of my invention depend upon the following principles:In an electric motor with armature and field-circuits independent, thetotal power which can be developed and the economy and efficiency of themotor are entirely independent of the strength ofthefield,but depend,within practical limits, alone upon the initial and counterelectro-motive forces and the resistance of the armature, if speed benot limited. The strength of the field determines the speed at which themotor must run to get a required efficiency. \Vith a given initialpotential at the armature-terminals, the speed may be maintainedconstant, no matter how the load varies from the maximum allowed, bychanging the strength of the field, such strength being diminished asthe load is increased, and, vice versa, increased as the load isdiminished. These principles, which I believe to be original with me,may be (ilemonstrated as follows: Consider the motor-current as derivedfrom mains having a fixed difference of potential, and the motor withits field and armature in shunt relation. In this case the armature runswith a velocity dependent upon the strength offield, the initialpotential, thenumber of turns, resistance, 8:c., of the armature, andthe load, and a counter electronlotive force is set up which diminishesthe armature-current. The higher the speed the greater this counterelectro-niotive force. Let E be the initial and e the counterelectro-motive force, and '2' the resistance of the armature. Thecurrent flowing in the arma ture is then XVith a given armature thetotal work done is the current expressed by The efficiency is the Itwill be seen that both these expressions-the total work done and theefficiencyare independent of any function of the field, but depend onlyon the initial and counter electro-motive forces and the resist ance ofthe armature, and any given value of 0 can be attained with any strengthof field by attaining proper speed. Suppose the motor doing a certainamount of work 1 at a certain speed. If ezgarmature- L current 18 andwork done Now, let the speed be increased one-half by diminishlng themechanical work per turn, the field re inaining the same. 0 now equalsE, current E 1 1S 4,? and work done which is less than before with samefield. Let the original field be strengthened one-hal f, the speedremaining I cal effect desired. and such mechanical effect the same. Thecounter electro-inotire force. current, and work done are the same as inlast case. Suppose, now, thatthis last field be decreased one-ninth andthe speed increased 7E 5E one-seventh. 6 now equals current is*.,

and work done 144,, although with weaver field. Or we may consider thespeed of machine constant, its field alone being varied. Differentiatingthe exefE-el more than in last case,

pression for work done, we have I] E If working with 0 less than thefield must be strengthened to increase the work done; but, except instarting a motor, this is the worst possible condition for working amachine, and hence is uneconomical and every way objectionable.

1n carrying my invention into effect I weaken the field by decreasingthe magnetizing effect of the field-magnet coils to produce an increaseof the mechanical eifectsthat is, of the speed or power, or both, of themotorand I strengthen the field by increasing the magnetizing effect ofits coils to decrease the said mechanical effects.

'While in the above mathematical demonstration I have, for convenience,considered the motor as in circuit with mains having a constantdifference of potentialas if, for instance, it were connected with amultiple-arc system of electrical distributionit will be evident thatthe same method is applicable to the regulation of the motor underchanges of potential in the circuit, for if an increased difference ofpotential occurs the field is strengthened to counteract it, and for ade creased difference of potential the field is correspondinglyweakened.

In all the different conditions and uses, as I have already stated, Ivary the magnetizing effect of the field-coils to vary mechanicaleffects in the motor. The different conditions and purposes for which Imake use of this method are as follows:

To change the speed or power of a motor on a circuit of constantpotential, the speed or power is increased by weakening the field, whichproduces a decreased counter electromotive force and an increasedarmature-current, and consequently the increased mechaniis greater thanif dc isnegative-that is, if

decreased by strengtlieningthe tlrld, and thus increasing the counterelcetro-niotive force.

To maintain the speed constant with at current of constant 1 oteutialunder varying loads. when the load increascs so that the speed wouldnaturally decline, the field is weakened, t ie counterQltt'fl'O'lllUllYb force diminished and armattire-current increased. thetendency to reduced speed is counteracted. and there is an increase inthe mechanical ct'fcetpower. Foradecreasrd load the field isstrengthened, the counter eleetro motive force increases, the currentdecreases, thes jieed remains the same, and the power is decreased.

To maintain speed or power constant under varying initial potential, ifthe potential at the motor terminals increases. these mechanical effectsincrease or tend to increase. By strengthening thev field I produce anincreased counter electro-motive force, so that the illcreased powerorSpeed, or the tendency thereto, is counteracted. and this counteractingmay evidently be itself considered a decrease in mechanical e fect,whether the regulation is performed simultaneously with the increase ofpotential or before or alter such increase. If the regulation isperformed simultaneously, with a gradual change of potential, there maybe less change in counter electro-motive force or armatin-e-currcnt; butthere is still the counteracting ofthe tendency to increased mcchaniealeffect, which counteracting is, I have just said, itself a decrease ofi'ncchanical effect. For a decreased or decreasing initial potential,the field is weakened to counteract the decrease in mechanical effectwhich would otherwise occur, and therefore to produce an increasedmechanical effect.

In any of the above cases I may, at the same time that I vary themagnetizing effect of the field-magnet coils,vary also thearmaturecurrent, whereby an additional effect is produced. In my PatentNo. 295.454. dated March 1S, 1884-, is set forth a method of varyingthefield of a motor by the use of adjustable independent field-coils.This is shown in connection with means for varying the relation betweenthe number of field-coils in series and those in shunt relation with thearmature to vary the armature-current.

I have devised another and a preferable mode of field regulation byvarying the magnetizing effect of the field-coils, which also maybe usedin connection with the abovemcntioned armature regulation; and this,while especially adapted for motors, is also applicable to theregulation of the field-magnets of dynamo-electric generators. According to this method I wind the field-coils in two sets or ranges, eachconnected with the supplying-circuit at one end, and having the otherend free. connecting the free end of each range to different points ofthe opposite range, more or less of the coils are placed in parallelcircuit with each other, and the resistance of the field, andconsequently the current and magnetizing effect of the field-coils, arevaried. 1f the armature is in shuntrelation with a part of thefield-coils, as in thepatent referred to, this also incidentally affectsthe armaturecircuit. The same commutator may be employed for varying thefield and for varying the armature-current in the manner set forth inthepatent referred to.

The field regulation or both field and armature regulation may be2LC('Oll']])ilSlld automatically by devices controlled by variations inthe speed of the motor. Thus a constant speed is maintained.

The figures of the accompanying drawings are diagrams illustrative ofthe principles and features of my invention, and I will describe thesame in detail.

Figures 1 and 2 represent the arrangement set forth 1n the patentreferred to. (J O are main conductors. a a is the field-circuit, and (ta a the armature shunt. In Fig. 2 the armature is shunted around a lessnumber of field-coils, the difference of potential at itscircnitterminals is lessened, and it receives less current, and thespeed or power is diminished; but by my new method I may accomplish thisregulation without changing the armature-terminals. This is illustratedin Figs. 3 and 4. The field-coils are broken at terminalspp,and by asuitable commutator, which will be presently described, greater or lessportions of the coils are progressively thrown into multiple arc witheach other, to decrease the resistance, strengthen the field, anddiminish the speed, and progressively removed from such relation toproduce a contrary effect. In this arrangement the armature-teiuninalsare considered as fixed.

Figs. 5 and 6 show the same arrangement of field with the armaturecapable of being shunted around a greater or less number of thefield-coils, illustrating the fact that the present mode of regulationmay be used in connection with that set forth in the patent referred to.Incidentally this regulation of the field has an increased effect by theincrease or diminution ofthe armature-current, d ue-to the increase ordiminution ofthe resistance around which it is shunted; but by using thefield and armature regulation together an enormous etfect may beproduced on the speed of the armature. By a very slight change theracing of the armature, even if the whole load is suddenly thrown off,is prevented. HowkVQl', the regulation of the field alone gives completecontrol of the motor for all practical purposes.

Fig. 7 illustrates the commutator and connections employed with the newmethod of regulating the field. O C are the main conductors, and c c 0&c., are sections of fieldcoils. The commutator is composed of a circleof metal blocks, d d d d, &c., two of which are extended into the arcs eand c. The connections from the field-sections are made, the

first and last to single and opposite blocks (2 of the commutator, andeach of the others to two blocks, (8 (Z and d d. The pivotedcommutatorarm consists of an insulating central portion, B, and metalextensionsff. These ends each bear on one of the arcs and upon therangeot'contacts. The field-current from 0 passes to h. where (in the presentposition of the arm) it divides. part passing to contact (Z extension f,are e, and coils c, to the reunitingpoint h. The rest passes throughcoils c to contacts (1, are 0, extension f, and contacts (1* d, to h. Itwill be seen that coils c and c" are thus placed in multiple are to eachother. By moving the commutator-arm in one direction or the other, moreor less of the sections of field-coils in which the magnet is wound aremnltiple-arced upon each other, the magnetizing effect of such coils isvaried, and the strength of the magnet is increased or diminished. Fig.8 shows this arrangement in connection with that for changing therelation between the sections of field-coils in series and those inshunt relation to the armature set forth in the patent referred to. Herethe additional arms Z Z, insulated from each other, bearing on thecontact-blocks, and passing under the arm B, are employed. The terminalsof the armature M are connected, respectively, with these arms. As thearms Z Z are moved the armature is shunted around agreaterorlessnumberot'the field-coils,remaining in series with theremainder. The arms B and H may work simultaneously, ifdesired.

By the use of the commutator shown in Fig. 8, the armature-current orthe strength of the field, or both, may be regulated, the circuits neverbeing broken, no adj ustable resistances being employed, and all thefield-coils being constantly in circuit, while their magnetizing effectis varied.

Fig. 9 illustrates an automatic arrangement which may be employed formoving the arm B to maintain a constant speed. A eentrifugal goternor,F, is connected with the motor-shaft, so as to be'aifected by variationsin speed. its moving collar carries two contact-arms, m m, insulatedfrom each other, and connected, respectively, with the conductors O C.These arms enter between the three arms a a 12%, which also areinsulated from one another.

G is a small electric motor, one of whose terminals is connected withthe two arms a if, the other with arm n. The motor-shaft is connected bya worm-gearing or other slow ing-down gearing with the arm B. Theconnecting-spindle is, for convenience of illustration, broken off andlaid out in dotted lines. An adjustable weight, H, is employed, so thatthe governor can be set to hold the contact-arms centrally at the normalspeed of the motor, to be regulated for its proper efficiency. Should avariation in the load cause the speed to slightly decrease, thegovernorballs fall and the arms make their lower eon-t tacts, closingcircuits to motor G, and causing it to revolve in a direction to shiftthe arm B, to decrease the field strength, and so keep the spe d at itsnormal point. When, on the con trary, the speed slightly increases,circuit is closed to the motor G in the opposite diree tion, and themovement of the arm B causes an increase in the field strength, whichkeeps the speed still at the normal.

As has been already explained, the same mode of regulation is applied tochange the power or speed of the motor with a constant current or tomaintain speed or power constant in a varying potential circuit.

The particular mode of regulation herein described and the apparatusused therein are not claimed herein, as they will form the subject of aseparate application, and I do not limit myself thereto.

The present application relates only to the method of regulation byvarying the magnetizing effect of the field-coilsthat is, in any way bywhich the magnet-coils or the current energizing the magnet is affected.

What I claim is 1. The method of regulation for an electrodynamic motorwhose main field-coils are in shunt relation to its armature, whichconsists in strengthening the magnetizing effect of the field-magnetcoils of the motor to decrease the mechanical effects, as speed orpower, or

both, and, vice versa, weakening such mag- FRANK J. SPRAGUE.

lVitnesses:

H. W. SEELY, T. G. GREENE.

